"The investigation by Deloitte's forensic unit found that, contrary to the rules of the lock-up, information on the bank's decision to cut the OCR [official cash rate] was transmitted by a Newshub Mediaworks reporter to several people in the Newshub office from the media lockup for the Monetary Policy Statement on 10 March," the RBNZ said in a statement.

The information was then passed to an economics blogger, who alerted the RBNZ after the official announcement, the statement said.

RBNZ Governor Graeme Wheeler said in the statement, "The leak is a serious and disappointing breach of many years of trust. It created the opportunity for improper gain on financial markets and damage to the integrity of the bank's communications."

There was no evidence that the leak led to any financial market impact, the statement said.

In the wake of the investigation, the central bank said it would stop providing media with embargoed copies of its interest rate decisions and other key documents ahead of the official release.

"The decision not to provide lock-ups for media or analysts means that these parties will receive the information at the same time as other financial market and public audiences," the statement said.

At its March 10 meeting, the RBNZ surprised markets by cutting interest rates by 25 basis points to a record low 2.25 percent, which pushed the New Zealand dollar (NZD=) down sharply.